The exterior walls of many commercial and industrial buildings are formed by mounting a number of wall panels and attached perimeter extrusions on a grid framework of structural members attached to the building. The resulting grid of wall panels are aesthetically attractive and protect the building structure from fluids in the terrestrial environment.
In designing a wall panel mounting system, there are a number of objectives. First, the joints between the wall panels should be substantially sealed from terrestrial fluids. Penetration of terrestrial fluids behind the wall panels can cause warpage and/or dislocation of the wall panels, which can culminate in wall panel failure. Second, any sealing material used in the joints between the wall panels should be nonskinning and non-hardening. The sealing material is located in a confined space in the joint. To maintain the integrity of the seal between the wall panels when the panels expand and contract in response to thermal fluctuations and other building movements (e.g., seismically induced movements), the sealing material must be able to move with the wall panels without failure of the seal. If the sealing material hardens or "sets up", the sealing material can break or shear, thereby destroying the weather seal. Third, the longevity of the sealing material should be at least as long as the useful life of the wall panels. Fourth, the sealing material should be capable of being pre-installed before erection of a wall panel beside a previously installed wall panel to provide for ease and simplicity of wall panel installation and low installation costs. Wall panel systems presently must be installed in a "stair step" fashion (i.e., a staggered or stepped method) because the sealing material must be installed only after both of the adjacent wall panels are mounted on the support members. Fifth, a drainage system or gutter should be employed to drain any fluids that are able to penetrate the seal in the joints. The gutter, which commonly is a "U"-shaped member in communication with a series of weep holes, must not overflow and thereby provide an uncontrolled entry for terrestrial fluids into the interior of the wall. During storms, winds can exert a positive pressure on the wall, thereby forcing terrestrial fluids to adhere to the surface of the wall (i.e., known as a capillary attraction). In other words, as the fluids follow the wall profile, the fluids can be drawn through the weep holes into gutter. The amount of terrestrial fluids drawn through the weep holes is directly proportional to the intensity of the storm pressure exerted on the wall exterior. If a sufficient amount of fluids enter the weep holes, the gutter can overflow, leaking fluids into the wall interior. Such leakage can cause severe damage or even panel failure.